Prior lock constructions have included arrangements for disengaging the lock cylinder plug from the turn bar including insertion of a tool when disengagement is desired. Exposed apertures have been proposed to receive such tools (U.S. Pat. Nos. 2,008,668, 2,027,731, 2,079,588, 3,019,633). Door sets including two such assembled have been proposed to be brought together from either side of a door and held in permanent engagement using interengaging prongs mounted on the subassemblies (U.S. Pat. Nos. 671,943, 2,726,891, 2,929,649, 3,048,436, 3,853,341). U.S. Pat. No. 3,048,436 states that subassemblies can be separated after permanent engagement using a strong pulling force which may cause damage. Security of such a lock is compromised.